The instant invention relates to a fluidized bed apparatus for mixing, drying, granulating, pelleting, varnishing, and/or coating pulverous or granular material, comprising a vessel which is at least approximately rotationally symmetrical with respect to an at least approximately vertical axis of the vessel and includes a lower part having a downwardly decreasing diameter, a dish which is at least approximately rotationally symmetrical with respect to the axis of the vessel and includes an at least approximately cylindrical wall into which opens the lower part of the vessel, an immersion tube protruding axially from above into the vessel and being immersed in the dish such that a narrow annular space is defined between the immersion tube and the cylindrical wall of the dish, and a diverting shield arranged at least approximately rotationally symmetrically around the immersion tube in an upper area of the vessel, gas introduced from above into the dish being deflected upwardly by the same, flowing through the annular space into the vessel and moving material contained therein, especially fluidizing the same, and the material entrained further in upward direction by the gas being deflected again by the diverting shield.
In a known fluidized bed apparatus of this kind (EP-A-0 103 894) the narrow annular space within the dish has a mean diameter which is much smaller than the mean diameter of the maximum free ring cross section of the vessel. The flow of gas exiting from the annular space in upward direction into the vessel entrains the material upwardly all around the immersion tube. It is deflected outwardly by the diverting shield and moved once more into the vicinity of the dish along the downwardly converging inner wall of the lower part of the vessel. From this location the material is entrained again in upward direction all around the immersion tube. This results in uniform rolling over of the material contained in the vessel. If the flow velocity of the gas is sufficient, this rolling motion passes over into a kind of complete fluidization of the material.